In the fields of optics and electronics, higher integration density, information of higher density, and image information with higher definition are required increasingly. For this reason, films with finer structures are strongly desired in such fields. In the medical field, the films with fine structures (microstructures) are also desired, for example, films that provide scaffolds for the cell culture, and membranes used for hemofiltration.
Examples of the microstructure films include films with honeycomb structures in which a plurality of micropores at a μm level are arranged in a honeycomb-like manner. To produce the honeycomb-structure film, a solution in which a predetermined polymer compound is dissolved in a hydrophobic organic compound is cast, and droplets are formed in a surface of a casting film by condensation. Such droplets are evaporated concurrently with evaporation of the organic compound (for example, see Japanese Patent Laid-Open Publication No. 2002-335949). The film produced in the above method is called a self-assembled membrane from formation behavior of its microstructure.
Conventionally, humidified (moist) air is condensed for forming droplets so as to form a porous structure. However, since condensation is a natural phenomenon, it is difficult to precisely control the extent thereof, and exact temperature control is necessary for uniform condensation. Therefore, improvements in forming of the droplets are desired.